Chamber for ultrasonic aerosol generation

ABSTRACT

A sanitary chamber is described which operates at room temperature to nebulize or aerosolize a liquid utilized in inhalation therapy. The chamber is a disposable thin walled flexible reservoir for containing a supply of liquid and for dispensing breathable gas such as air in admixture with the liquid. The chamber includes a flexible diaphragm responsive to ultrasonic vibrations of an abutting electroacoustic transducer for admixing the liquid and gas. The chamber further includes integrally formed dispensing means which serves to direct the emanating gas-liquid admixture in an ascending vortex pattern to promote evaporation at ambient temperature. In a particular embodiment, the chamber comprises an inflatable bag constructed of low-cost plastic film material which lends itself readily to compact and sterile storage and disposal.

BACKGROUND OF THE INVENTION

This invention relates to ultrasonic liquid nebulizing apparatus foratmospheric humidification and more particularly to a chamber forgenerating an ambient temperature aerosol within a room or the like foruse in inhalation therapy.

In the treatment of respiratory diseases, techniques are employed whichinvolve the inhalation by the patient of aerosols. Conditionsaccompanying many respiratory diseases are respiratory congestion andinadequate expulsion by the patient of secretions from the lungs. It hasbeen found that a water or saline aerosol introduced into the lungs atroom temperature assists in relieving and in correcting theseconditions. It is conventional practice to directly introduce amedicine, such as a relaxant for treatment of asthma, into the humanrespiratory system in aerosol form.

Humidifiers, as they are commonly known, are of two general varieties:hot liquid vaporizers and cool vapor aerosol generators. Aerosolizers ornebulizers for cool vapor generation utilized in inhalation therapy havegenerally included a reusable reservoir provided with a supply of liquidand a supply of breathable gas under substantial pressure. In one type,a liquid discharge nozzle and a gas discharge nozzle are typicallyarranged so that a stream of the gas is discharged past the liquid toprovide a mixture of gas and nebulized liquid for breathing by thepatient. In another type, a whirling blade is disposed to dipintermittantly into the liquid supply thereby lifting the liquid intothe path of a stream of transport gas. These conventional types ofnebulizers frequently do not produce aerosol particles of uniformlysmall character or cause evaporation which would result in deep relaxingpenetration of the aerosol into the respiratory system. Nebulizers haverecently been developed which utilize ultrasonic acoustic techniques foraerosol generation. See, for example, U.S. Pat. No. 3,861,386.

A major problem associated with cold vapor respiratory therapy is theavoidance of contamination of the generated vapor by impurities carriedby the recirculated ambient air. As the air recirculates through theliquid containing chamber, contaminants accumulate which can ultimatelycause the transmitttal of a concentration of dangerous infectants. Inthe past, it has been the practice to frequently sterilize the vaporgenerator, especially the liquid reservoir, and then provide the liquidsupply with a suitable disinfectant. Therefore, relatively frequent,expensive and somewhat cumbersome servicing of the vapor generator isrequired in order to maintain the requisite high standard of sanitation.

SUMMARY OF THE INVENTION

The above-noted and other disadvantages associated with conventionalnebulizers are avoided by use of a nebulizer of the present invention inwhich the contaminant exposed element of the nebulizer is disposable. Inparticular, the nebulizer according to the invention comprises adisposable chamber for containing a supply of therapeutic liquid and fordispensing breathable gas such as ambient air in admixture with theliquid. The chamber includes a flexible diaphragm responsive toultrasonic vibrations of an abutting electroacoustic transducer foradmixing the liquid and the gas, and further includes a dispensing meansintegrally formed in the upper wall of the chamber which serves todirect the emanating gas-liquid admixture in an ascending vortex patternto promote evaporation at ambient temperature.

In one preferred embodiment, the chamber is a collapsible bag offlexible plastic film which inflates to a desired shape duringoperation. In particular, the nozzle means of the flexible gas chambercomprises a ring of arcuate slits in a wall of the chamber above thenormal liquid level wherein the slits form inwardly facing flapsdisposed to direct the fluid admixture toward the center of the ring.Further, the plane of the ring is arranged to be transverse of thenormal circulating fluid flow within the chamber. The center of the ringis maintained at a depressed orientation relative to the periphery ofthe ring by a strap trying opposing sides, i.e., the upper and lowerwalls, of the flexible bag. A small orifice in the depression providesdrainage of accumulated condensate back into the reservoir. Thisprevents liquid sputtering at the output slits which would otherwisegenerate undesired discontinuities and non-uniformities in the nebulizedoutput. The depression additionally assures the creation of a horizontalradially inwardly directed component of the nebulized output.

Accordingly, it is one of the purposes of the present invention toprovide an apparatus for generating an aerosol from a liquid by means ofultrasonic waves. In particular, this invention provides a sanitaryaerosol generator and air scrubber for medical application. The aerosolsso generated have a relatively uniform particle size. In addition, thenebulizer inhibits the transmittal of accumulated contamination byproviding an inexpensive nebulizing chamber which is disposable.

A particular feature of the nebulizer according to the invention is anovel fluid dispensing nozzle integrally formed in a disposable package.A separate reusable structure is not needed so the requirement offrequent and relatively expensive sterilization procedures iseliminated.

Another purpose of the invention is to provide a sterile nebulizingchamber which is easily stored, transported and discarded. This purposeis achieved by providing a collapsible (i.e., inflatable) chamber madeof an inexpensive plastic film material integrally incorporating allrequisite fluid inlet and outlet features and acoustic coupling featuresnecessary for providing the desired aerosol output.

In addition to the foregoing purposes, objects and advantages, theinvention possesses other advantages set forth in the followingdescription of preferred embodiments of the invention. These featuresare illustrated in part by the drawings accompanying the specification.It is to be understood, however, that variations in the embodiments maybe made without departing from the scope of the invention as set forthin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view of one form of the ultrasonic nebulizerembodying the present invention showing the major components thereof anda first preferred embodiment of a nebulizing chamber;

FIG. 2 is a vertical elevational view in partial cross-sectionillustrating a second preferred embodiment of a nebulizing chamberaccording to the invention;

FIG. 3 is a side-elevational view in partial cutaway and cross-sectionillustrating the first preferred embodiment of the nebulizing chamber;and

FIG. 4 is a top elevational view in partial cutaway showing the secondpreferred embodiment of the chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An ultrasonic nebulizer 10 according to the invention comprises fourcomponents, an ultrasonic wave generator or oscillator 12, a liquidsupply reservoir 14, a gas source inductor 16, and a nebulizing chamber18. The nebulizer 10 may be secured in a unitary housing 20 having anopen-topped basin 22 for partially containing the nebulizing chamber 18.The basin 22 may include a bottom wall 24 in which is mounted anelectroacoustic transducer 26, and the liquid supply reservoir 14 may bedisposed adjacent and slightly elevated relative to the basin 22 andincluded a liquid outlet conduit 28 which leads to the basin 22.

The gas source 16 may comprise a fan 30, an inlet opening 32, an airfilter 34, and an outlet nozzle 36. The outlet nozzle 36 is preferablydisposed to direct a flow of air horizontally along a side of the basin22 and thus along a side wall of chamber 18.

The ultrasonic oscillator 12 is preferably of the type commonly used forproducing tuned, relatively high-power electromagnetic radio frequencyenergy. The radio frequency output of the oscillator 12 is coupled tothe electroacoustic transducer 26, which may be a wafer of piezoelectricceramic crystal. The crystal transducer 26 is suitably resilientlymounted to permit free vibration when radio frequency energy from theoscillator 12 is impressed thereupon.

Turning now to FIG. 2, there is shown one embodiment of a nebulizingchamber 118 suitable for placement in the basin 22. The chamber 118,which may be of substantially transparent plastic film includes a lowershell 38 and an upper shell 40 joined along a seam 42. The lower shell38 includes four side panels 44 and a bottom panel 46. The lower shell38 or merely a portion of bottom panel 46 may be formed of thinnersubstantially more pliant material than other portions of the chamber118. The thinner region is preferably offet from the center and intendedto be juxtaposed with the crystal transducer 26 as a pliant diaphragm48. The diaphragm 48, which may have a thickness of up to about 0.005inch, provides minimal structural support for the lower shell 38 and isadapted to intimately contact the transducer 26 when the chamber 118 ispartially filled with liquid. The seam 42 may rest upon the lip of thebasin 22 (FIG. 1) to furnish additional structural support.

The upper shell 40 comprises side panels, 50, 52, 54 and 56, top panel58 and a lateral extension 60. As seen most clearly in FIG. 4, thelateral extension 60 is offset from the center of panel 56. Theextension 60 is adapted to mate with an air nozzle 136 (shown in phantomin FIG. 2) of a fan (not shown).

Top panel 58 defines a relatively large central circular opening 62 ofrelatively large diameter. The circular opening 52 includes a raisedflange 64 with a radially inwardly extending lip 66. A removablefrustroconical baffle 68 mates with the flange 64 from the inner side ofupper shell 40. The rim of the baffle 68 includes a castellation 70defining a pattern of radially disposed orifices between the raisedflange 64 and the baffle 68. The baffle 68 includes a cylindricalprojection 72 at the apex of the cone which served as a knob formounting the baffle 68 to the central opening 62.

Referring to FIG. 4, in conjunction with FIG. 2, the castellation 70 isformed by a plurality of columns 74 extending outwardly from the surfaceof the baffle 68 defining radially inwardly directed outlets 76 betweeneach adjacent column 74. The nozzle cross-section at the inlet, i.e.,the outer radial edge of the baffle 68, is approximately equal to thenozzle cross-section at the outlet, i.e., facing the projection 72, andthe length of the nozzle is approximately equal to the minimum width.Thus, in conjunction with the radially inwardly extending lip 66 whichforms the top of the outlet 76, the inlet portion has a relatively deepU-shape and the outlet portion has a relatively shallower U-shape. Inorder to prevent the accumulation of moisture and condensate in thenozzle outlet area on the surface of the baffle 68, the trough of theoutlets 76 are below the level of the surface of the insert so they alsoserve as drainage means for accumulated moisture on the surface of thebaffle 68. Thus, runoff can be in virtually any direction into thenebulizing chamber 18 if the housing 20 is substantially level. To aidin alignment of the baffle 68 within the central opening 62, each of thecolumns 74 is provided with a shoulder 78 which mates with the raisedflange 64 and radially extended lip 66.

In operation, the chamber 118 filled with liquid to a desired levelreceives air through the extension 60, which directs flow in a generallyhorizontal circulating pattern. An ultrasonic frequency is impressedupon the transducer 26 which vibrates the diaphragm 48 causingcavitation in the adjacent liquid. Bubbles stream to the surface whichtransforms to a mist at the liquid gas interface. The gas flow conveysthe mist to the outlet area. Upon encountering the flange 64 and lip 66,the flow is directed horizontally inwardly in a corkscrew pattern overthe external surface of the baffle 68. The exhaust flow defines vortexascending from the apex of baffle 68 which enhances the evaporation ofthe mist. In particular, the ascending, swirling mist substantiallyevaporates upon contact with air to produce the desired humidificationof the ambient atmosphere.

Turning now to FIG. 3, another embodiment of the nebulizing chamber 18is illustrated. The view of FIG. 3 shows the chamber 18 shown in FIG. 1in a side elevation.

The chamber 18 comprises a collapsible, i.e., inflatable bag 80, ofrelatively thin pliant material substantially impervious to liquidpenetration. The bag 80 has an upper panel 82, a lower panel 84, and aside panel 86. The side panel 86 comprises a rectangular sheet joined ona seam 88 at opposing ends to form a tube. The upper and lower panels82, 84 may be approximately octagonal, or more precisely, square-shapedsheets with truncated corners 85 and joined along the margins of thesheets to the side panel 86. The upper panel 82 encloses one end of thetube and the lower panel 84 encloses the opposing tube end. The lowerportion of the bag 80 generally conforms to the shape of the basin 22upon inflation.

The bag 80 may be a pliant plastic film material generally impervious towater. Suitable materials are polyethylene, nylon, cellophane, polyvinylchloride, or Mylar (a DuPont trademark). A wide range of wallthicknesses is satisfactory for the side panel and the top panel. Forexample, a nominal wall thickness of 0.006 in. to 0.020 in. providesadequate strength and durability. The membrane and lower panel 84, whichconfronts the transducer 26 and serves as a flexible diaphragm, ispreferably as thin as possible in order to prevent undue loss of usefulenergy to flexure-induced heating. A practical upper limit or membraneis about 0.005 in. The preferred membrane thickness is on the order of0.001 in. or even less. The membrane thickness is limited only by theavailability of ultra-thin material generally impervious to liquid.

Within the side panel 84 of the bag 80 are two openings. The firstopening is generally circular orifice 90 which leads directly into theinterior of the bag 80. The orifice 90 may be spaced about half wayabove the bag lower margin and is preferably located near a verticaledge 92 between corresponding truncated corners 85. A collar 94circumscribes the orifice 90 and includes external flaps 96. The orifice90 is provided as an inlet for pressurized gas, such as air, which isadapted to mate with the nozzle 36 of a gas supply, such as a fan 30(FIG. 1). The collar 94 permits the nozzle 36 to be tied by a strap 97or otherwise secured by the flaps 96 to the nozzle in a mannerminimizing gas leakage.

The orifice 90 is located near the edge 92 so that the gas inlet 90 isoffset to produce a horizontally circulating gas flow pattern within thebag 80. The bag 80 may also have a circular cylindrical cross-section.In such case, the nozzle 36 of the gas supply is mounted at an offsetangle through the side panel 86, and the inlet orifice 90 may beelliptical in shape or otherwise shaped to accommodate and angularlymated gas nozzle 36.

The second side panel opening is a vertical tube 98 which serves as aliquid supply inlet and which may be formed by an overlaid strip bondedto the side panel 86. The tube 98 has an external end 100 located abovethe bottom of the bag 80 and an internal end 102 opening into the bagand located adjacent the bag bottom. The liquid outlet conduit 28(FIG. 1) is adapted to be inserted into the tube 98. A ring seal 31around the outlet conduit 28 provides a substantially airtight contactbetween the tube 98 and the conduit 28.

The outlet of the nebulizing chamber is located in the upper panel 82. Aplurality of slits 104 is cut in the upper panel 82 to define protrudingflaps or tongues 106. The slits 104 may be arcuate, and the tongues 106are preferably arranged in an inwardly facing ring so that they form aradially inwardly facing pattern of aerosol outlet openings.

Between the center of the upper panel 82 and the lower panel 84 is aretaining strap 108 which controls the height of vertical inflation ofthe bag 80. The length of the strap 108 is shorter than the height ofthe bag side panel 86 so that a central depression 110 is establishedwithin the ring of outlet openings in the upper panel 82 upon fullinflation of the bag 80. This depression assures a radially inwardlydirected exhaust through the outlet openings. A small drain hole 112 islocated near the center of the depression 110 so that any moisture whichmay collect at the exit of the slits 104 drains from the depression 110.This arrangement assures that moisture does not interfere with theaerosol flow through the slits 104.

The operation of the nebulizer 10 according to the invention may bevisualized with reference to FIG. 1. The bag 80 is filled through tube98 with a liquid to be nebulized from reservoir 14 to a preselectedlevel below the height of the gas orifice 96. The fluid level may bemaintained relatively constant by a level sensitive valving arrangement(not shown). As an alternative to filling the bag through tube 98, thebag may be pre-filled with a measured amount of liquid to be nebulized.The liquid to be nebulized may be water, water containing a suitabledisinfectant or some other suitable medication in liquid form.

The electroacoustic transducer 26 is excited at ultrasonic frequency byan electrical signal from the oscillator 12. The transducer wafer 26oscillates axially of its face while it is held in intimate contact withthe lower panel 84 by the weight of the liquid within the bag 80. Theoscillating crystal induces waves in the liquid which are transmittedthrough the liquid to the surface to cause the surface to undulate. Inaddition, a pressure drop occurs in the liquid near the face of theoscillating transducer 26 which causes formation and collapse ofcavities or bubbles at an extremely high rate. The bubbles stream towardthe surface of the liquid where, upon encountering the interface of thegas and the liquid, a fine mist or aerosol is generated.

Gas, i.e., filtered air from the fan, 30, is supplied through the gasorifice 90 and directed in a generally horizontal circulating pattern120 over the surface of the liquid. The force of the gas creates acirculating pattern which captures liberated aerosol and conveys it tothe outlet openings 104 in the upper panel 82. The aerosol is expelledthrough the slits 104, which cause the tongues 106 to lift. A backpressure at the outlet openings maintains the bag 80 in an inflatedcondition. Additionally, the location of the slits 104 in an inwardlyfacing ring near the center of the nebulizing chamber, in conjunctionwith a gas circulating pattern having a substantial converginghorizontal component, further enhances the mist generation efficiency ofthe nebulizer by releasing the mist to the atmosphere in an ascendingcorkscrew pattern which promotes evaporation of the mist upon mixturewith the ambient air. The nebulizer may generate as much as 600 to 800ml per hour at optimum operating efficiency and optimum liquid level.However, as the liquid drops below the optimum level, the efficiency ofthe nebulizer decreases markedly. Since a period of several hours isrequired to exhaust all liquid by nebulization after the liquid surfacedrops below the optimum level, changes in the output of the apparatuswill be apparent long before the liquid is exhausted. Thus, theapparatus can be serviced long before damage is done to the apparatusthrough overheating or the like.

The optimum liquid level approximately corresponds to a multiple of thehalf wave length of the excitation frequency in the liquid medium. Aliquid level of about 3 cm within a chamber about 25 cm in height issatisfactory where the excitation frequency is about 1.4MHz.

Attention to the size and number of slits assures that adequate backpressure is maintained for inflation of the bag at the volume flow ratesof interest. For example, for an air volume throughput of 25 to 100 CFM,a satisfactory outlet arrangement is approximately twelve slits,arranged in a circular ring of about four inches in diameter, each slitbeing a full semicircle of about 7/16 in. radius.

In order to maintain reasonable air purity at high throughput rates, aHEPA (High Efficiency Particulate Air) type filter may be employed atthe air intake.

Various means may be employed to provide transport gas. For example, afan, gas from an external compressor, gas from the plenum of an airconditioner or furnace, or gas from a pressurized tank may be suppliedto the nebulizing chamber.

A fan system is perhaps most practical and convenient especially inenclosed rooms. Where room air is recirculated, the device including anair filter may serve as an air scrubber to remove contaminants such assmoke from the atmosphere.

Having illustrated the invention with reference to specific embodiments,other embodiments will be apparent to those of ordinary skill in theart. The invention should therefore be limited only as indicated by theappended claims. For example, the nebulizing may be supplied with apremeasured quantity of liquid to be nebulized so that an externalreplenishing source would be unnecessary. Thus, upon exhaustion of theliquid supply, the chamber could be discarded.

We claim:
 1. A nebulizing chamber for use with an ultrasonic electroacoustic transducer adapted to interface with said chamber, said chamber comprising:a thin-walled inflatable bag adapted to enclose a liquid and having outlet means comprising a plurality of slits forming flaps in the upper, normally horizontally disposed chamber wall, wherein said slits are arranged in a ring with the arcuate flaps disposed to direct said exhaust radially inwardly so as to generate an ascending convergent outlet flow pattern wherein said chamber includes a retaining means maintaining a depression within said ring upon inflation of said chamber for directing a portion of said exhaust in a convergent, substantially horizontal direction.
 2. A nebulizing chamber for use with an ultrasonic electroacoustic transducer adapted to abut said chamber, said chamber comprising:an inflatable bag of thin plastic film having top and bottom walls, side walls, a liquid inlet passage, and a gas inlet passage, said gas inlet passage being in a side wall and and disposed to permit introduction of transport gas in a generally horizontally circulating flow pattern; outlet means in the top wall for dispensing a gas/liquid aerosol mixture, said outlet means comprising a plurality of arcuate slits arranged in a ring so as to form a plurality of radially inwardly disposed openings with inwardly directed flaps; a strap tying the bottom wall to the top wall at a location within the ring to form a depression in the ring upon bag inflation for maintaining a radially inwardly directed outlet flow component to promote an ascending vortex pattern of aerosol; and a hole within the depression for draining accumulated moisture.
 3. A nebulizing chamber adapted to abut an electroacoustic transducer within an enclosing cavity, said chamber comprising:a collapsible bag having all walls constructed of a thin, flexible plastic film material, said bag being adapted to inflate to a desired shape at least partially defined by said enclosing cavity only upon induction of pressurized gas into said bag and further being adapted to enclose a supply of liquid, a wall of said bag adapted to abut an ultrasonic transducer; outlet nozzle means integrally formed in a wall of said bag above the normal liquid level of said bag, said nozzle means comprising perforations in said film material of a size sufficiently small to provide a back pressure to assure inflation, wherein said perforations of said outlet nozzle means comprise arcuate slits arranged in a ring in said top wall, said slits defining arcuate flaps disposed to direct exhaust from said nozzle means in a convergent direction.
 4. A nebulizing chamber according to claim 3 further including means disposed within said ring for returning condensate to the interior of said bag. 